HYUNDAI SANTA FE ENGINE PROBLEM

2003 Hyundai Santa Fe • 6 cylinder AWD Automatic • 125,000 miles

My wife 2003 Santa Fe Hyundai recently Started to Idle on its own up to 3000rpms when it is started up. It is doing this on its own. I was checking the fluids today and it also did this. I stepped on the gas pedal and it started to decrease in speed but then agin started to rise on its own what could be causing this. Timing belt etc replaced recently could this have an effect on the acceleration.